Always download repos when they are being patched

[vyasr]

Description

This PR updates rapids_cpm_find to force downloading of a package whenever a nonempty patch command exists.

Checklist

• I am familiar with the Contributing Guidelines.
• New or existing tests cover these changes.
• The documentation is up to date with these changes.
• The cmake-format.json is up to date with these changes.
• I have added new files under rapids-cmake/
  • I have added include guards (include_guard(GLOBAL))
  • I have added the associated docs/ rst file and update the api.rst

[vyasr]

@robertmaynard this is close, but there is an issue with passing an empty patch command. The issue comes from passing empty strings to rapids_cpm_find and how they are parsed by cmake_parse_arguments, which seems to drop that string even if it is quoted in the rapids_cpm_find function call. I tried using the cmake_parse_arguments(parse_argv 0...) syntax instead, but that causes the cpm_find-options-escaped-* tests to fail because quotes around CPM args are no longer preserved. I'm not sure what the best approach is here and could use some advice.

[robertmaynard]

@robertmaynard this is close, but there is an issue with passing an empty patch command. The issue comes from passing empty strings to rapids_cpm_find and how they are parsed by cmake_parse_arguments, which seems to drop that string even if it is quoted in the rapids_cpm_find function call. I tried using the cmake_parse_arguments(parse_argv 0...) syntax instead, but that causes the cpm_find-options-escaped-* tests to fail because quotes around CPM args are no longer preserved. I'm not sure what the best approach is here and could use some advice.

@vyasr I tried playing around as well and I don't see a great solution to this. I think we are going to do is change around rapids_cpm_generate_patch_command to generate the entire CPM/FetchContent string of PATCH_COMMAND <....> or an empty string. Therefore we only pass a PATCH_COMMAND arg when we truly have a patch.

That would mean a change to each rapids_cpm_find invocation in rapids-cmake/cpm but it should be pretty easy:
PATCH_COMMAND ${patch_command} becomes ${patch_command}

[vyasr]

/merge

[jakirkham]

Thanks all! 🙏